Always keep current instruction pointer in a register

lib/evmone/analysis.hpp

@@ -86,7 +86,6 @@ struct instr_info;
 
 struct execution_state
 {
-    const instr_info* next_instr{nullptr};
     evmc_status_code status = EVMC_SUCCESS;
     int64_t gas_left = 0;
 
@@ -113,10 +112,10 @@ struct execution_state
     evmc_revision rev = {};
 
     /// Terminates the execution with the given status code.
-    void exit(evmc_status_code status_code) noexcept
+    const instr_info* exit(evmc_status_code status_code) noexcept
     {
         status = status_code;
-        next_instr = nullptr;
+        return nullptr;
     }
 };
 
@@ -134,7 +133,7 @@ union instr_argument
 
 static_assert(sizeof(instr_argument) == sizeof(void*), "Incorrect size of instr_argument");
 
-using exec_fn = void (*)(execution_state&, instr_argument arg);
+using exec_fn = const instr_info* (*)(const instr_info*, execution_state&);
 
 /// The evmone intrinsic opcodes.
 ///

lib/evmone/execution.cpp

@@ -22,22 +22,16 @@ evmc_result execute(evmc_instance*, evmc_context* ctx, evmc_revision rev, const
 
     auto state = std::make_unique<execution_state>();
     state->analysis = &analysis;
-    state->next_instr = &state->analysis->instrs[0];
     state->msg = msg;
     state->code = code;
     state->code_size = code_size;
     state->host = evmc::HostContext{ctx};
     state->gas_left = msg->gas;
     state->rev = rev;
-    while (state->next_instr)
-    {
-        const auto& instr = *state->next_instr;
-
-        // Advance next_instr to allow jump opcodes to overwrite it.
-        ++state->next_instr;
 
-        instr.fn(*state, instr.arg);
-    }
+    const instr_info* instr = &state->analysis->instrs[0];
+    while (instr)
+        instr = instr->fn(instr, *state);
 
     evmc_result result{};